Optimus 51 Fettle

I began fettling this stove recently and have had a few issues. The pump cup leather was shot so I replaced it. The I noticed that it wasn't holding pressure and kicking kerosene back out of the NRV so I promptly replaced it. If you have read my earlier post you know that I only get about four pumps before the filler cap seal leaks also (gotta order parts). What is odd is that once I changed the NRV it now makes an unusual noise when pumped. It does pump and no kero seeps out. I have changed the NRV again to see if it was a faulty one from the manufacturer and no luck. Mine have the lead washer btw. I even tried adding some copper anti-seize compound to the NRV threads and that made the sound go away for about ten pumps but it came back. I do not know if the stove made this sound before as it would not build pressure when originally tested. Btw, the NRV is"two fingers tight" on the wrench because I did not want to strip the threads with the anti-seize compund added (over torque it).

For clarification the sound is like air bubbling inside a pressure container. An echoing type of hollow sound. It may be due to my leaking filler cap seal but I am unsure. Has anyone else experienced something like this ? The dunk test shows no leaks coming from the NRV or pump area just the filler cap seal.

Hi @Cookie the NRV and base of the pump are below the fuel level level in the tank. When you pump and air enters the tank it has to bubble its was through the kerosene to get to the air space above the liquid. Perhaps you are hearing this air entering the tank as bubbles?

If you pump air into a tank with the filler cap removed you will certainly hear the bubbles of air rising through the liquid...

@kerophile Thanks for that information. I did in fact have the cap off to watch for bubbles and since the seal is bad it may very well be the issue. The other stoves have seals that are much less functional and yet did not make the noise. Perhaps it's because it is the largest of the stoves in question and thus the volume of the tank amplifies it even more. Now that I think of it perhaps the tank not being completely full (50-60%) wasn't a big help either.

@kerophile I agree 100% on not filling the stove as much as possible. I mention the 50-60% fill capacity simply to indicate that I may have had the chamber with just enough fuel above the NRV area to allow a large bubble to easily form when actuating the pump and thus have ample space above it in which to allow the reverberating sound to echo.

Today I removed the nrv (this is the second one tried), checked the lead seal (it looked ok), replaced the lead seal with another new one, pumped it with my thumb over the fill tube. It held pressure and made no noise in doing so. Once I removed my thumb air rushed out. I replaced the filler tube cap, primed, and pumped. Almost immediately the hollow sound was heard while pumping again. Perhaps this is just a noisy stove ? This is with the original burner installed.

I am having an issue with the burner. After a very good pre-heat it will ignite but will only stay running when an open flame is present beneath it (at the jet) such as while pre-heating or with a long lighter. I filled the pre-heating cup to the max, lit the alcohol, and placed a windscreen around the burner. Just before it went out I pumped it a few times. It sprang to life but I immediately noticed the at the burner tube at the jet was glowing red. I assumed that that was a sign of under burn and shut it down. There was still some alcohol burning for a few seconds. After cooling I swapped the burner with a known and tried 210 burner. It ran like a champ with this burner. I'd even dare say that it ran better on the 51 than on the 210. The 51's burner has new seals, been extensively blown out by air, and has a new jet in it. Perhaps my method of lighting the stove caused the under burn but I can not get it to run otherwise. Any ideas ?

Can you confirm that you have a Primus No. 51 please? That is only my guess but there is no such model as Optimus 51.

You see, you mention under burn which is a pesky problem with silent burners…. (a Primus 51 is a roarer burner, originally)
under burn: so, do you have a silent burner (w/o regulator valve)?

You describe "... the burner tube at the jet was glowing red." <-- that could be a roarer burner? Certainly a problem there but would not be considered under burn as far as I know.

You then installed a burner off of a 210 onto your 51. 210 is a 1 pint roarer. Primus 51 is a 1 3/4 pint roarer. Both roarers, I don't recall what's involved with that swap. I would have thought they were a large vs small burner. I don't have either in-hand at the moment...

Including pics is always a most effective method when engaging membership seeking answers.

There are many opportunities for me not to get it right above, so help a guy out and please do firm up those details for us.
If posting pics is a problem, then that's an unfortunate factor going forward but not a show stopper.
carry on, thank you, best regards omc

By the way, make sure both inner and outer caps are free of debris, anything that is likely to provide a glowing ember point, a wipe with a rough cloth should get rid of any flakes, just run a finger round all surfaces, if there are any 'catches' get rid of em.

@kerophile Thanks. I have a No 5 and this is the procedure that I use to ignite the stove

@Simes
1) You are correct in that the stove is a Primus 51 and not an Optimus 51. That was an error on my part

2) It is a roarer burner. The stove will only run when an open flame is presented at the jet after pre-heating. Due to this condition I was trying to use the last seconds of the pre-heat to ignite the fumes just as the pre-heat alcohol went away hence why I used the term "under burn". Doing so is causing the inside tube where the nipple is mounted to get very hot (red) if the pre-heating alcohol runs for say five to ten seconds. I know that this is not the preferred method of lighting the stove. I can pre-heat the dickens out of the stove, close the air valve, pump it 8-10 times, light the fumes with a lighter, and literally have to use a lighter to maintain the fumes ignition. No open flame and she hisses out immediately. The burner head is definitely hot and there is plenty of fuel coming out as it is roaring full tilt with the lighter held at the nipple. My only hint so far is I noticed a small flame at the base of the nipple. I have tried three new nipples so far and each one has felt like the threads in the burner may be stripped and allowing gas to pass by hence the occasional tiny flame. At this point I am beginning to suspect that the previous owner may have damaged the nipple threads in the burner and that may be the cause of the issue but I am still working on it.

3) There is nothing fancy involved in swapping a primus 210 and a 51's roarer burner. The riser tubes threads are a match on the tank side. It's a simple twist one off and twist the other on.

Ok....so apparently this old fool didn't realize just how much pre-heating was required in a larger burner since he (who shall remain nameless ) is used to his 210's, 123R, and 00 sized roarers. I fixed the pressure leak after this video by screwing the burner head onto the vaporizing/riser tube (?) fully. Apparently when I replaced all of the seals, pump leather, and nrv I didn't screw it on 100%. You can see at 4:04 the little flame kick out from the base of the nipple. That nipple already has some copper anti-seize on it in an effort to help seal it. It at least runs now. The burner tube at the nipple did not glow or get excessively hot this time.

Hi @Cookie thank you for the additional information and photos of a lovely Pr.51 roarer burner stove.
I now understand how you were able to run the smaller burner, intended for a 1pint Pr.210 on a 1.75 pint Pr.51. @OMC

You shifted both burner and its riser tube across!

The Pr.210 and Pr.51 share a taper thread female tank fitting so as long as the male taper on the riser fits, the burner/riser combinations are interchangeable between tanks.